As in many other areas of technology, wireless communication is becoming increasingly popular also in industrial process control. Some of the main standards for wireless communication in wireless control of an industrial process utilise protocols that are time-slotted. In time-slotted protocols each superframe comprises a plurality of time slots, wherein each sensor is allotted a specific time slot for wirelessly sending measured process variable data for example to a gateway. Time-slotted wireless protocols used in industrial control, such as WirelessHART and ISA 100, have a predefined number of time slots per superframe. In WirelessHART each superframe may for example be 1000 ms, of which 500 ms may be dedicated to sensor time slots while the remaining 500 ms is dedicated to administration, e.g. for broadcasting information to the sensors. Each time slot dedicated to the sensors may for example be 10 ms. Thus, according to this example only 50 time slots per superframe are dedicated to sensor measurements, giving a maximum of 50 sensors to communicate with a gateway in one superframe. However, since it is generally desirable that most sensors send measurement data several times in a superframe for robustness the number of sensors than can be used in an industrial control sensor node network interface system with each gateway is further limited. Typically several gateways have to be provided for large sensor node networks, with each gateway having a plurality of sensors associated with it. If several gateways are used the gateways should be synchronized, especially if one controller is associated with several gateways.